<template>
  <div class="spec-preview">
    <img :src="imgsrc" />
    <div class="event" ref="event" @mousemove="moveTo"></div>
    <div class="big" >
      <img :src="imgsrc" ref="bImg" />
    </div>
    <div class="mask" ref="mask"></div>
  </div>
</template>

<script>
import throttle from 'lodash/throttle'
  export default {
    name: "Zoom",
    props:['imgsrc'],
    mounted() {
      },
    methods: {
      moveTo:throttle(function(e) {
        let {mask, bImg, event} = this.$refs;
        bImg.style.left = -e.clientX + 'px';
        bImg.style.top = -e.clientY + 'px';
        let left = e.offsetX - mask.clientWidth / 2;
        let top = e.offsetY - mask.clientHeight / 2;
        if (left < 0) left = 0; 
        else if (left > event.clientWidth - mask.clientWidth / 2) left = event.clientWidth- mask.clientWidth / 2;
        if (top < 0) top = 0; 
        else if (top > event.clientHeight - mask.clientHeight / 2) top = event.clientHeight - mask.clientHeight / 2;
        mask.style.left = left + 'px';
        mask.style.top = top + 'px';

      })
    }
  }
</script>

<style lang="less">
  .spec-preview {
    position: relative;
    width: 400px;
    height: 400px;
    border: 1px solid #ccc;

    img {
      width: 100%;
      height: 100%;
    }

    .event {
      width: 100%;
      height: 100%;
      position: absolute;
      top: 0;
      left: 0;
      z-index: 998;
    }

    .mask {
      width: 50%;
      height: 50%;
      background-color: rgba(0, 255, 0, 0.3);
      position: absolute;
      left: 0;
      top: 0;
      display: none;
    }

    .big {
      width: 100%;
      height: 100%;
      position: absolute;
      top: -1px;
      left: 100%;
      border: 1px solid #aaa;
      overflow: hidden;
      z-index: 998;
      display: none;
      background: white;

      img {
        width: 200%;
        max-width: 200%;
        height: 200%;
        position: absolute;
        left: 0;
        top: 0;
      }
    }

    .event:hover~.mask,
    .event:hover~.big {
      display: block;
    }
  }
</style>